R�g�n�ration, diff�renciation et hormones de mues chez l'embryon de blatte en culture in vitro

Physiological and molecular mechanisms of insect appendage regeneration

Regeneration, as a fascinating scientific field, refers to the ability of animals replacing lost tissue or body parts. Many metazoan organisms have been reported with the regeneration phenomena, but showing evolutionarily variable abilities. As the most diverse metazoan taxon, hundreds of insects show strong appendage regeneration ability. The regeneration process and ability are dependent on many factors, including macroscopic physiological conditions and microscopic molecular mechanisms. This article reviews research progress on the physiological conditions and internal underlying mechanisms controlling appendage regeneration in insects.

Metabolism of ecdysteroids in the female tick Amblyomma hebraeum (Ixodoidea, Ixodidae): accumulation of free ecdysone and 20-hydroxyecdysone in the eggs

[3H]-20-hydroxyecdysone ([3H]-20E) injected into Amblyomma hebraeum females 7 days before the beginning of oviposition, viz. at the beginning of vitellogenesis, was converted to 3 polar peaks of unknown nature called 1, 2 and 3, and to apolar conjugates AP1, AP2 and AP3. AP2 have the same retention times as the esters of 20E with long chain fatty acids described in Ornithodoros moubata (Diehl et al. 1985). However, principally unmetabolized 20E was incorporated into the ovaries, and 16% of the injected labelling was recovered in the eggs, 3/4 being free 20E. When 20E was injected during oviposition, it was not converted to the polar products but only to the apolar products. At this time, 76% of the total radiolabel injected accumulated in the egg-batch, principally in the form of free unmetabolized 20E. After injection of [3H]-ecdysone ([3H]-E), the three polar metabolites 1', 2' and 3', probably 20-deoxy homologues of 1, 2 and 3 described above were always produced irrespective of the time of injection. In addition, E was metabolized to 20E and to the apolar conjugates AP1, AP2, and AP3. E, 20E and peak 2' were incorporated into the ovary within the first day after injection. These 3 compounds were found in freshly laid eggs in variable proportions, the quantity of E decreasing with time while 20E and peak 2' increased. At the end of oviposition, ca. 60% of the injected radiolabel had been incorporated into the eggs. Apolar products and polar metabolites accumulating in the body were apparently not used as a source of free hormone for the eggs. Our results with tritiated ecdysteroids confirm our data concerning endogenous ecdysteroids of the eggs of A. hebraeum (Connat et al. 1985). This species, in contrast to 2 other female ticks, Ornithodoros moubata and Boophilus microplus, incorporates free E and 20E instead of ecdysteroid conjugates into its eggs. The role of these free ecdysteroids remains to be elucidated.

Sensory receptor differentiation and axonal pathfinding in the cercus of the grasshopper embryo

An immunological probe selective for insect neurons (L.Y. Jan and Y.N. Jan, 1982, Proc. Nat. Acad. Sci. USA 79, 2700-2704) was used to characterize the genesis of sensory neurons and the formation of the peripheral nerves in the grasshopper cercus. During embryogenesis the cercal ectoderm produces a characteristic set of sensory neurons in a precise spatiotemporal order. The first neurons migrate from the epidermis into the lumen and send out axons toward the CNS along the epidermal wall. These luminal neurons arise in four distinct groups, each of which establishes a separate branch of the cercal nerve, with the axons of the three distal groups converging onto the cell bodies of the more proximal neurons and thus seeming to use them as an intermediate target on route to the CNS. Epidermal neurons, whose cell bodies remain within the epithelium, begin to appear at a later stage. These cells come to innervate external sensory hairs, and in general their axons grow to the CNS along the preexisting nerves. Each sensory hair possesses two nonneuronal cells--the trichogen (shaft-forming) and tormogen (socket-forming) cells--which also stain with the antibody and begin to display immunoreactivity at the same time as the allied sensory neuron. The trichogen and tormogen cells do not form the hair shaft and socket until much later, with outgrowth occurring in an order quite distinct from that in which the receptors undertook their initial, biochemical differentiation. Thus, these two aspects of trichogen/tormogen differentiation appear to be under separate developmental control.